Wednesday, March 16, 2005

346: Evolution of hemichordates

Years ago, there was a hypothesis to link the two. Their common ancestor was a wormlike crawler with tentacles called the Lophenteropneusta, and there were suspected representatives of this 'missing link' photographed on the deep sea floor. The worms crawl on the surface of the mud, slurping it in one end and excreting it out the other, leaving behind looping trails of tubelike fecal material. These abyssal worms were thought to have tentacles, but the results of a new paper in Nature show that this is not the case, which means that these worms are 'just' enteropneusts, and the morphology of the common ancestor of the two hemichordate classes is once again wide open. That's not so terrible, though; what's interesting are these fascinating new enteropneust species that Holland et al. have found.

Testing and revising evolutionary hypotheses of the evolution of hemichordates.